Isolation and serotyping of porcine rotaviruses and antigenic comparison with other rotaviruses

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Abstract
Seven rotavirus strains were isolated in cell cultures from the intestinal contents of piglets with diarrhea. Rhesus monkey kidney MA104 cells with pancreatin in the cell culture medium was the host system of choice for virus isolation and replication. A cell culture immunofluorescence test in which MA104 cells were used in microtiter plates was very effective for detecting and assaying rotaviruses. A plaque reduction neutralization test, cross-protection studies in gnotobiotic pigs and electrophoresis of rotaviral double-stranded RNA were used for comparing viruses. Three strains produced plaques on initial isolation attempts, replicated well in cell cultures, and were antigenically very similar. Apparently, these 3 strains should be considered porcine rotavirus serotype 1, with The Ohio State University (OSU) [USA] strain serving as the prototype. The OSU strain was distinct from bovine, simian, canine and human (Wa and M) rotaviruses by plaque reduction neutralization. Four strains did not produce plaques on initial isolation attempts, were difficult to adapt to cell cultures, and were related to each other but were distinct from the serotype 1 strains. The Gottfried (G) strain should be tentatively considered as a prototype for porcine rotavirus serotype 2. The G strain was antigenically closely related to canine and simian rotaviruses and less so to human M rotavirus (human rotavirus serotype 3). Canine, simian and human M rotaviruses were closely related. All 7 porcine rotavirus strains caused diarrhea in gnotobiotic pigs. Cell-cultured vaccines of the OSU and G strains caused only mild or no diarrhea in gnotobiotic pigs, and protection occurred when such pigs were challenged with homologus, but not heterologous, virulent viruses. A survey indicated that 94% of 274 procine serum samples and 100% of 74 herds were serologically positive to the porcine OSU rotavirus.